2.4. Activation of NPCs to Synthesize and Secrete SDF-1α in the Proinflammatory Culture In Vitro

To mimic the proinflammatory microenvironment of the degenerative IVD, NPCs (1 × 10⁵ cells/well) were incubated in serum-free medium containing 10 ng/mL IL-1β (PeproTech, Rocky Hill, NJ, USA) and 50 ng/mL TNF-α (PeproTech) for 48 h. The secreted SDF-1α in the supernatant was evaluated using enzyme-linked immunosorbent assay (ELISA), while the adherent NPCs were used for real-time RT-PCR.